This invention relates in general to substance detection devices and in particular to a new and useful device for determining the concentration of a substance which has a paramagnetic property.
The invention particularly concerns a device for the determination of the concentration of substances with paramagnetic properties, particularly oxygen, in substance mixtures, comprising a cell assembly divided into several chambers, which revolve relative to a device for producing a magnetic field that penetrates the cell assembly, and a coil assembly associated with this device, which converts the magnetic induction produced in it by the paramagnetic substance into an electrical signal.
A similar device of this type is known from the German OS No. 1924228. The known device has a revolving cell assembly which is divided into several chambers and moves in the air gaps of two permanent magnets at a constant rpm. An electrical coil winding is attached about the yoke of each permanent magnet. In the presence of substances with paramagnetic properties in the measuring chambers of the cell assembly, the substance molecules within the magnetic fields produced by the permanent magnets orient themselves to varying degrees and induce an electrical signal in the coil assemblies, the intensity of which corresponds to the concentration of paramagnetic substances in the respective chamber of the cell assembly to be analyzed. The induced measuring signal is highly dependent on the magnetizing force produced by the permanent magnets. Every change or disturbance of this magnetic field results in a measurable and undesirable vitiation of the measuring signal. Interferences may occur, for example, when the air gaps of the magnet yokes are different in width. These gap widths may typically change during the measuring operation by not more than 10.sup.-8 mm, if a change in the measuring signal gap widths is to be less than 1% by volume O.sub.2. External disturbing fields penetrate the cell assembly and vitiate the measuring result in an undesirable manner. An additional possible interference is the transfer of vibrations, e.g. due to the revolving cell assembly, or also due to shocks in the environment, to the permanent magnets, which stimulate these, together with the electrical signal coils, to start oscillatory motions, which alter the gap width of the permanent magnets and thereby produce a measuring signal in the signal coils (microphonic effect).